A novel procedure for identification of 3D moisture diffusion parameters on thick composites: theory, validation and experimental results

This paper presents a novel method for the identification of the parameters governing Fickian moisture diffusion in composite materials. In the first part of the manuscript, the theoretical background is given and closed-form solutions are produced for 3D Fickian diffusion. Then, the different existing identification alternatives are reviewed and a novel procedure is proposed that takes advantage of all the gravimetric curve data points instead of just initial slope and saturation. The method relies on the solution of an optimization problem. In the second part of the paper, validation of this identification technique is performed from simulated gravimetric curves. The main advantage of the method when compared to previously published materials is that diffusion coefficients and saturation level can be identified from gravimetric curves obtained from unsaturated coupons. This is particularly useful when considering thick coupons that will take a long time to saturate or when non-Fickian diffusion mechanisms occur after some time. Finally, the method is applied to experimental results obtained from glass/epoxy composites. It is shown that although the diffusion of moisture in the composite is basically non-Fickian, it can be considered Fickian up to about 10 days and that these data are sufficient to retrieve the 3D diffusion coefficients as well as the Fickian saturation level.